Crossword Genius

Scared of a phantom leaving for a ball (6)

Ross

I believe the answer is:

aghast

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'scared' is the definition.
(thesaurus)

I cannot understand how the remainder of the clue works.

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(Other definitions for aghast that I've seen before include "Appalled, shocked" , "Filled with fear or horror" , "What's carried in bag has teacher" , "Stupefied with horror" , "Filled with consternation or horror" .)

I've seen this clue in The Hindu.
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